When visiting a new city, you might recall specific spots, like a serene
garden or a bustling café. However, it usually takes a few days for you to
intuitively connect these places into a cohesive understanding of the area.
A recent study by neuroscientists at MIT’s Picower Institute for Learning
and Memory sheds light on how the brain constructs such “cognitive maps” and
highlights the critical role of sleep in this process.
For decades, scientists have known that specialized neurons called “place
cells” in the hippocampus help the brain encode specific locations. However,
forming a mental map of how these locations connect is more complex. First
proposed in 1948, cognitive maps describe how we mentally organize spaces into
navigable networks. The new research, published in Cell Reports,
reveals that weakly attuned neurons in the hippocampus play a crucial role in
assembling these maps by coordinating activity over several days, with sleep
playing a vital role.
Building the Map: The Role of Weakly Spatial Cells
In the study, led by Wei Guo from Professor Matthew Wilson’s lab, researchers
introduced mice to simple mazes. Over five days, the mice explored freely for
30 minutes a day. The team recorded the neural activity in the hippocampus,
focusing not only on the prominent place cells but also on the activity of
“weakly spatial” cells, which are less directly tied to specific locations.
Using advanced techniques like manifold learning, the researchers found that
weakly spatial cells progressively became more synchronized with patterns of
activity in the hippocampal network. Over time, this synchronization allowed
the brain to stitch together individual locations represented by place cells
into a comprehensive map of the maze.
“These weakly spatial cells act as bridges, linking distinct places into a
continuous mental framework,” says Guo. By Day 5, the mice’s brains encoded a
functional map of the environment, enabling them to navigate more intuitively.
The Power of Sleep in Learning
To understand sleep’s role, the team compared two groups of mice exploring a
maze twice in one day. One group was allowed to sleep during a three-hour
break, while the other group stayed awake. The results were striking: only the
mice that slept showed significant improvement in their neural maps. Sleep
appeared to consolidate and refine the connections between weakly spatial
cells and place cells, enhancing the brain’s ability to represent both
individual locations and their relationships.
“Sleep allows the brain to replay experiences, which strengthens and organizes
memories,” explains Wilson. Without sleep, the weakly spatial cells failed to
meaningfully integrate into the network.
Beyond Physical Maps: Adding Meaning to Spaces
Interestingly, the cognitive maps formed by the mice were not exact blueprints
of the mazes but abstract representations. These mental maps allow the brain
to navigate and plan without physically being in a space. For example, after
forming a map of your hotel’s neighborhood, you might mentally plan a morning
walk to a nearby bakery and imagine enjoying your treat in the park.
Wilson hypothesizes that weakly spatial cells might also integrate non-spatial
information, like the significance of landmarks or objects, adding layers of
meaning to cognitive maps. While this study didn’t include landmarks or test
specific behaviors, future research could explore how these cells enrich our
understanding of environments.
Implications for Human Learning
This study underscores the brain’s ability to learn and organize information
through natural exploration and sleep, without reinforcement or rewards. Such
“implicit learning” may be fundamental to how humans acquire knowledge and
adapt to new environments.
“This research highlights a fascinating aspect of neural plasticity,” the
authors write. “Understanding these processes could provide new insights into
how we learn, remember, and navigate the world.”
The study was supported by the Freedom Together Foundation, The Picower
Institute, and the National Institutes of Health.
A new study conducted by researchers at Cambridge University has uncovered
the vital role that dietary fiber plays in strengthening the body’s immune
system. The research focuses on how the intake of fiber-rich foods, such as
whole grains, fruits, vegetables, and legumes, supports the growth of
beneficial gut bacteria, which are crucial for protecting the body against
infections.
